Mieczyslaw Metzger

Both the continuous and batch stirred tank reactors, considered as the control plants, are ones of the most frequently investigated processes. The classical irreversible exothermic reaction, taking place in the reactor, is a great challenge faced by the automatic control engineers due to the nonlinear and non-stationary behaviour of this process. A very interesting control problem deals with the working-point regime of this process in which an open-loop operation is unstable. Therefore, for this kind of processes, there is a need to develop the sophisticated low-level control algorithms and then to compare their performance with the classical PID controller.

The idea of the structure of this pilot plant is shown in Fig. 1.

Simplified scheme of the pilot plant

Figure 1. Simplified scheme of the pilot plant

 

In the real-world plants the equipment for measurement of the substrates and products concentrations are very expensive and in majority of cases it is impossible to obtain the continuous or discrete measurement data of these parameters. Therefore only the inlet and outlet temperature can be considered as the controlled variables since the temperature can be easily measured on-line.

When only temperature measurement data is accessible and the temperature inside the reactor is the controlled variable, the process of the cooling of the exothermic chemical reactor with the application of the cooling jacket can be considered as the heat exchange process. Therefore it is possible to carry out the process only with the water inside the reactor tank. The heat, produced in the reactor due to the exothermic chemical reaction that should take place inside the reactor, can be simulated by means of the computer-controlled electric heater (see Fig. 1). This approach allows us to ensure the low costs of the experiments and to avoid the problem of the security standards due to the operating of the chemical reaction.

It is important to note that the temperature sensors, the flow meters and the control valves with actuators are the real industrial equipment - only the heat produced due to the reaction taking place is simulated.

A new pilot plant has been designed and carried out in the Control Systems and Control Equipment (CSCE) Group at the Institute of Automatic Control. This plant includes the hybrid stirred tank reactor with electric heater simulating the heat generated by the reaction.

The pilot hybrid stirred tank reactor is designed in a special manner that it will be possible to incorporate this new stirred tank reactor to existing heat distribution installation. The simplified scheme of the extended pilot plant is presented in Figure 1.

It is possible to connect the jacket of the chemical reactor into the heat distribution pilot plant to ensure the possibility of adjusting the inlet jacket temperature and the possibility of heating and cooling of the reactor jacket by means of two existing heat exchangers (see Fig. 1).

The reactor must be heated by the jacket for initialisation of the reaction, whereas it must be cooled when the exothermic reaction takes place (which will be simulated by controlled heater in the reactor).

The switching valves in the system presented in the Figure 1 allow to operate the reactor as a part of the heating circuit (see Figure 2a) and as an independent plant with cooling circulation from municipal water supply (see Figure 2b). For quicker heating the additional thermal source can replace heat exchanger (see Figure 2c).

In all cases the reactor itself can be operated in the batch mode or in the continuous mode. The reactor with control equipment is shown in Fig.3.

Major possibilities of the jacket heating and cooling

Figure 2. Major possibilities of the jacket heating and cooling.

 

Pilot plant with electronic control equipment

Figure 3. Pilot plant with electronic control equipment. 1) the reactor with electric heater; 2) power controller for electric heater and signal transmitters for temperature sensors; 3) programmable smart transmitters for flow sensors; 4) power supplies for current loops; 5) temperature sensors at the inlet and outlet of the reactor and its jacket.